1. Field of the Invention
The invention relates to physical asperity testing of disk drive systems. More specifically, the present invention relates to manners of detecting a fly height margin using controlled excitation of air bearing modes.
2. Description of the Related Art
Computer systems generally utilize auxiliary storage devices onto which data can be written and from which data can be read for later use. A direct access storage device is a common auxiliary storage device which incorporates rotating magnetic disks for storing data in magnetic form on concentric, radially spaced tracks on the disk surfaces. Transducer heads driven in a path generally perpendicular to the drive axis are used to write data to the disks and to read data from the disks.
Many aspects of development and manufacturing in the disk drive industry are involved in the effort to produce the most reliable direct access storage device possible while maintaining a reasonable price. These efforts include design, component selection, development tests, and manufacturing tests. Once produced, disks are generally submitted to a variety of manufacturing tests. For instance, a series of testing operations are typically carried out on each disk. These operations may be conducted at a common station, or the disk may be transported to different stations to perform the specified operation.
One such operation involves conditioning the disk surface. The conditioning involves abrasive objects wiping or dragging across the surface of the disk. The purpose of this operation is to remove any residue or physical asperities. A further operation is a touchdown height test. The touchdown height is the height of a flying head sensor over the surface of a disk at which the head first begins to contact asperities. The touchdown height may be measured with the use of a test head gimbal assembly (HGA) flying above the disk. In manufacturing, a fly height margin is designated and defined to be a safe operating height of above the highest asperity on the disk. To determine the fly height margin, a speed sensitive HGA is used to gauge the height of the asperities on the disk surface. The actual touchdown height of the HGA is critical for determining a fly height margin.
The disk drive industry has been engaged in an ongoing effort to increase the densities of hard disk drives. The ultrahigh densities have allowed the disk drive industry to continually miniaturize disk drives. A common problem inherent to ultrahigh densities is the fly height of the read/write head. As the density is increased, the fly height margin of the read/write head must be reduced. If the fly height margin is substantially greater than the ideal fly height, the read/write head's capability to accurately and reliably read and write data will be diminished. Thus, the fly height margin becomes an important measurement of the quality of the disk.
Glide or fly height margin testing detects the asperities and other abnormalities that are detrimental to the performance and reliability of the disk drive. Typically, a glide height calibration apparatus includes a disk, an HGA, and a calibrated asperity. The HGA is velocity sensitive, or in other terms, the fly height of the HGA is dependent on the linear velocity of the disk. Currently, in order to determine the fly height the velocity of the disk is reduced until the slider attached at the end of the HGA makes contact with the calibrated asperity.
Once the slider contacts the calibrated asperity, a small piezoelectric ceramic crystal (not shown) detects the vibration caused by the impact. When contact is made between the calibrated asperity and the slider of the HGA, the impact is translated from a vibration caused by the impact into an electrical signal by the piezoelectric ceramic. At that point the fly height is calibrated to the height of the calibrated asperity.
Several problems have arisen from calibrating the glide height in the manufacturing process. One problem associated with the glide test is the inability to measure the fly height accurately due to inadequate measurement tool accuracy and repeatability. One current process includes multiple optical fly height measurements and repeated adjustment of parts to meet the optimal fly height specification. One of the adjustments is a mechanical adjustment of the suspension of the HGA. This form of adjustment consequently can cause damage and yield fallout. Additionally, certain components can become unstable after adjustment and begin to creep back to their original mechanical state.
Other problems that current fly height tests suffer from include fly height variation due to slider wear during calibration and measurement, and instability in the surface due to lube change. Furthermore, the manufacturing time required to perform measurement and adjustment processes can be extensive, and the yield fallout due to the handling and the adjustment is costly. The resulting variation of fly height can be very large. With such a large variation, the calibration of the glide height results in significant yield fallout and adds to the uncertainty of the actual fly height.
Thus, it can be seen from the above discussion that there is a need existing in the art for an improved fly height adjustment and calibration method and apparatus.